1. Field of the Invention
The invention generally provides a method and an assembly for the production and use of an encoded sonar waveform. More particularly, the invention provides a method and an apparatus that produces a modulated sonar pulse, wherein the baseband waveform modulating the pulse is encoded so as to resemble noise.
2. Description of Related Art
Particularly in a time of war or anytime when a vessel is attempting to use sonar to collect information about an adversary, it is often desired that one's use of an active sonar system not be detected by the adversary. While there are methods of reducing the adversary's ability to detect the carrier wave of a traditionally modulated sonar pulse (such as through power management, pulse compression, directivity of transducer array, and tactical techniques), more sophisticated detection methods and equipment are readily designed and built which, to a large extent, can overcome these obstacles to detection by detecting the structure of the modulation within the modulated carrier wave. The regular variation of the modulating waveform (baseband waveform) can be detected even, for example, at low transmit signal power levels. With the proper electronic equipment, traditional, linear frequency modulated (LFM) sonar transmissions, for example, are readily detectable due to the regular nature of the modulation (a linear frequency ramp). Such detection of traditional modulation is achieved with use of so-called feature detectors, such as nth law and delay and multiply detectors.